The present invention relates to fluid controllers of the type used to control the flow of fluid from a source of pressurized fluid to a fluid pressure actuated device such as a steering cylinder which comprises part of a full-fluid-linked vehicle steering system.
Although the present invention may be used in connection with fluid controllers of many types, and having various applications, it is especially advantageous when used with a fluid controller of the type used in full-fluid-linked steering systems, and will be described in connection therewith.
A typical fluid controller of the type to which the present invention relates includes a housing which defines various fluid ports, and further includes a fluid meter, a valve means, and an arrangement for imparting follow-up movement to the valve means, in response to the flow of fluid through the fluid meter. The flow through the controller valve means is directly proportional to the area of the variable flow control orifices in the main fluid path, the area of the flow control orifices in turn being proportional to the rate at which the steering wheel is rotated.
A typical example of a vehicle which utilizes a fluid controller of this type would be an agricultural tractor or combine. There is growing interest in being able to steer such vehicles by some means other than the conventional rotary input of the steering wheel by the operator. For example, in vehicles designed for harvesting crops, there is a desire to be able to steer the vehicle by sensing the crop (e.g., rows of corn), and adjust the position of the steering cylinder accordingly so that the vehicle follows the crop rows.
Prior to the present invention, in order to provide a vehicle with both conventional rotary input, full-fluid-linked steering, and automated guidance, would have required that the vehicle be equipped with both a conventional fluid controller and a separate, parallel control system, operable in response to an electrical signal generated by the crop sensors. Such steering systems have not been commercially acceptable, primarily because of the cost associated with providing two separate, independent steering devices. However, another disadvantage of such a system is the difficulty and complexity of coordinating the two different devices. For example, if the automated guidance device is operating, and the vehicle operator realizes that for safety reasons it is necessary to deviate from the automated path, the conventional rotary input controller must be connected to the automated guidance device in such a manner that the controller is able to override the automated guidance device. Although such systems have been proposed, the overall expense and complexity has prevented commercial acceptability.